Password security

Passwords are an important part of any database security system. To be secure, passwords must be difficult to guess, and they
must not be easily accessible on users' hard drives or other locations. SQL Anywhere passwords are always case sensitive.
You can specify a function used for password authentication with the verify_password_function option. See verify_password_function option.

By default, passwords can be any length. For greater security, you can enforce a minimum length requirement on all new passwords
to disallow short (and therefore easily guessed) passwords. You do this by setting the min_password_length database option
to a value greater than zero. The following statement enforces passwords to be at least 8 bytes long.

When you create a configuration file, you can optionally include password information. To protect your passwords, consider
hiding the contents of configuration files with simple encryption, using the File Hiding (dbfhide) utility. See File Hiding utility (dbfhide).

The following example defines a table and function and sets some login policy options. Together they implement advanced password
rules that include requiring certain types of characters in the password, disallowing password reuse, and expiring passwords.
The function is called by the database server with the verify_password_function option when a user ID is created or a password
is changed. The application can call the procedure specified by the post_login_procedure option to report that the password
should be changed before it expires.

The code for this sample is also available in the following location: %SQLANYSAMP12%\SQLAnywhere\SQL\verify_password.sql.

-- This example defines a function that implements advanced password rules
-- including requiring certain types of characters in the password and
-- disallowing password reuse. The f_verify_pwd function is called by the
-- server using the verify_password_function option when a user ID is
-- created or a password is changed.
--
-- The "root" login profile is configured to expire passwords every 180 days
-- and lock non-DBA accounts after 5 consecutive failed login attempts.
--
-- The application may call the procedure specified by the
-- post_login_procedure option to report that the password should be changed
-- before it expires.
-- only DBA should have permissions on this table
CREATE TABLE DBA.t_pwd_history(
pk INT DEFAULT AUTOINCREMENT PRIMARY KEY,
user_name CHAR(128), -- the user whose password is set
pwd_hash CHAR(32) ); -- hash of password value to detect
-- duplicate passwords
-- called whenever a non-NULL password is set
-- to verify the password conforms to password rules
CREATE FUNCTION DBA.f_verify_pwd( uid VARCHAR(128),
new_pwd VARCHAR(255) )
RETURNS VARCHAR(255)
BEGIN
-- a table with one row per character in new_pwd
DECLARE local temporary table pwd_chars(
pos INT PRIMARY KEY, -- index of c in new_pwd
c CHAR( 1 CHAR ) ); -- character
-- new_pwd with non-alpha characters removed
DECLARE pwd_alpha_only CHAR(255);
DECLARE num_lower_chars INT;
-- enforce minimum length (can also be done with
-- min_password_length option)
IF length( new_pwd ) < 6 THEN
RETURN 'password must be at least 6 characters long';
END IF;
-- break new_pwd into one row per character
INSERT INTO pwd_chars SELECT row_num, substr( new_pwd, row_num, 1 )
FROM dbo.RowGenerator
WHERE row_num <= length( new_pwd );
-- copy of new_pwd containing alpha-only characters
SELECT list( c, '' ORDER BY pos ) INTO pwd_alpha_only
FROM pwd_chars WHERE c BETWEEN 'a' AND 'z' OR c BETWEEN 'A' AND 'Z';
-- number of lowercase characters IN new_pwd
SELECT count(*) INTO num_lower_chars
FROM pwd_chars WHERE CAST( c AS BINARY ) BETWEEN 'a' AND 'z';
-- enforce rules based on characters contained in new_pwd
IF ( SELECT count(*) FROM pwd_chars WHERE c BETWEEN '0' AND '9' )
< 1 THEN
RETURN 'password must contain at least one numeric digit';
ELSEIF length( pwd_alpha_only ) < 2 THEN
RETURN 'password must contain at least two letters';
ELSEIF num_lower_chars = 0
OR length( pwd_alpha_only ) - num_lower_chars = 0 THEN
RETURN 'password must contain both upper- and lowercase characters';
END IF;
-- not the same as any user name
-- (this could be modified to check against a disallowed words table)
IF EXISTS( SELECT * FROM SYS.SYSUSER
WHERE lower( user_name ) IN ( lower( pwd_alpha_only ),
lower( new_pwd ) ) ) THEN
RETURN 'password or only alphabetic characters in password ' ||
'must not match any user name';
END IF;
-- not the same as any previous password for this user
IF EXISTS( SELECT * FROM t_pwd_history
WHERE user_name = uid
AND pwd_hash = hash( uid || new_pwd, 'md5' ) ) THEN
RETURN 'previous passwords cannot be reused';
END IF;
-- save the new password
INSERT INTO t_pwd_history( user_name, pwd_hash )
VALUES( uid, hash( uid || new_pwd, 'md5' ) );
RETURN( NULL );
END;
ALTER FUNCTION DBA.f_verify_pwd SET HIDDEN;
GRANT EXECUTE ON DBA.f_verify_pwd TO PUBLIC;
SET OPTION PUBLIC.verify_password_function = 'DBA.f_verify_pwd';
-- All passwords expire in 180 days. Expired passwords can be changed
-- by the user using the NewPassword connection parameter.
ALTER LOGIN POLICY root password_life_time = 180;
-- If an application calls the procedure specified by the
-- post_login_procedure option, then the procedure can be used to warn
-- the user that their password is about to expire. In particular,
-- Interactive SQL and Sybase Central call the
-- post_login_procedure system procedure.
ALTER LOGIN POLICY root password_grace_time = 30;
-- Five consecutive failed login attempts will result in a non-DBA
-- user ID being locked.
ALTER LOGIN POLICY root max_failed_login_attempts = 5;